EP2221873B1

EP2221873B1 - Light emitting device

Info

Publication number: EP2221873B1
Application number: EP10150474.4A
Authority: EP
Inventors: don Song Hyun
Original assignee: LG Innotek Co Ltd
Current assignee: LG Innotek Co Ltd
Priority date: 2009-02-18
Filing date: 2010-01-12
Publication date: 2020-04-08
Anticipated expiration: 2030-01-12
Also published as: EP2221873A1; KR101007130B1; KR20100094243A; CN101807593B; CN101807593A; US20100207123A1; US8242509B2; WO2010095781A1

Description

BACKGROUND

Field

Embodiments as broadly described herein relate to a light emitting device.

Background

A light emitting device is a semiconductor device that converts current into light. A red light emitting device may be used as a light source for electronic devices, information telecommunication devices, and the like, together with a green light emitting device. One example of such light emitting devices is a light emitting diode (LED). Due to widespread use of such devices, improvements in reliability and performance of such devices is desirable.
EP 0 011 418 A1 and JP 2006 286991 A relate to the manufacture of monolithic arrays of light-emitting semiconductor diodes (LEDs) for electroluminescent display devices. In particular, JP2006 286991 A discloses a light emitting device comprising a plurality of light emitting elements arranged in a two-dimensional array and formed on a common second electrode layer, each light emitting element including a first conductivity type layer, an active layer and a second conductivity type layer. A plurality of trenches extend through the first conductivity type layer and the active layer thereby separating adjacent light emitting elements of the plurality of light emitting elements. An insulating layer is formed in the trenches between adjacent light emitting elements. First electrodes are respectively disposed on the plurality of light emitting elements and a common electrode electrically connects the first electrodes.

SUMMARY OF THE INVENTION

The invention relates to a light emitting device as defined in claim 1 and to a method of making a light emitting element as defined in claim 8. Further embodiments are subject of the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements wherein:

FIG. 1 is a plan view of a light emitting device according to an embodiment as broadly described herein;
FIG. 2 is a cross-sectional view taken along line II-II' of the light emitting device shown in FIGs. 1-2;
FIGS. 3 to 17 are process diagrams of a method for manufacturing the light emitting device shown in FIGs. 1-2; and
FIGS. 18 and 19 illustrate current spreading characteristics of the light emitting device shown in FIGs. 1-2.

DETAILED DESCRIPTION

Hereinafter, a light emitting device according to embodiments as broadly described herein will be discussed with reference to the accompanying drawings.
In the description of embodiments, when a layer (or film) is referred to as being 'on/over' another layer or substrate, it may be directly on/over another layer or substrate, or intervening layers may be present. Further, when a layer is referred to as being 'under/below' another layer, it may be directly under/below another layer, or one or more intervening layers may be present. In addition, when a layer is referred to as being 'between' two layers, it may be the only layer between the two layers, or one or more intervening layers may also be present.
Gallium nitride (GaN) semiconductors have high thermal stability and a wide bandgap that may be combined with other elements, such as, for example, In, Al, and the like, making it possible to manufacture a semiconductor layer that emits green light, blue light, and white light while easily controlling emission wavelength. As a result, the gallium nitride (GaN) semiconductor may be seriously considered in developing a high output electronic device including a light emitting device such as an LED.
A high current, such as, for example, 350mA or more, may be applied to a large area light emitting device. Current applied to an N-type electrode pad typically generates current spreading. However, when a high current is applied, current has straightness at the shortest distance with respect to a P-type electrode, rather than the current spreading described above, causing a current bottleneck phenomenon. The current bottleneck phenomenon may cause degradation of an Epi layer, leaving the device vulnerable to radiating characteristics if the device is driven for a long time in a high temperature environment.
A light emitting device in accordance with the exemplary embodiment shown in FIGs. 1-2 includes a second conductive semiconductor layer 130, an active layer 120, a first conductive semiconductor layer 110, a first insulating layer 150 that separates the first conductive semiconductor layer 110, the active layer 120, and the second conductive semiconductor layer 130 into a plurality of areas, first electrodes 160 that are formed over upper surfaces of the separated first conductive semiconductor layers 110, and a pad electrode 170 that is formed over the first insulating layer 150 to connect the first electrodes 160.
In certain embodiments, the second conductive semiconductor layer 130 may be approximately 100∼500 nm thick and may be made of materials such as, for example, GaN, InGaN, InAlGaN, AlGaN, InGaAlP, AlGaAs; the active layer 120 may be approximately 10∼100 nm thick and may be made of materials such as, for example, InGaN/GaN, InGaN/InGaN; the first conductive semiconductor layer 110 may be approximately 1000∼10000 nm thick and may be made of materials such as, for example, GaN, InGaN, InAlGaN, AlGaN, InGaAlP, AlGaAs; the first insulating layer 150 may be made of materials such as, for example, Oxide, Nitride, Polymer film; the first electrodes 160 may be approximately 10∼5000 nm thick and may be made of materials such as, for example, Cr, Ni, Ti, Al, Ag, Pt, Pd, Au ; and the pad electrode 170 may be approximately 100∼5000 nm thick and may be made of materials such as, for example, Cr, Ni, Ti, Al, Ag, Pt, Pd, Au . Other combinations of thickenesses and/or materials may also be appropriate.
As discussed above, in manufacturing a large area light emitting device, an electrode structure that can provide smooth current flow and avoid a current bottleneck phenomenon is needed. However, in the case of a vertical type GaN light emitting device, current applied to an electrode pad formed over an N-type electrode is light-emitted while spreading into a light emitting surface through an N-type electrode. As discussed above, in the case of the large area light emitting device, when a high current is applied, the current bottleneck phenomenon is caused.
In an embodiment in which parallel type electrode structures are formed over GaN LEDs, the structures may be separated in order to control the current bottleneck phenomenon caused due to the application of high current, making it possible to achieve smooth current spreading. Such a large area light emitting device may be structured so that luminous strength may be relatively uniformly distributed over the area by the smooth current spreading, and may prevent degradation of the Epi layer due to the current bottleneck wile also improving high-temperature reliability.
The general electrode structure may have a structure in which a wing electrode conforms to a pad electrode. Even in the separated case, since it is a serial type, the current bottleneck phenomenon may occur around the pad electrode when a high current is applied. Since the breakdown current spreading of the Epi layer is not smooth due to the current bottleneck phenomenon caused by the application of high current, the problems discussed above, such as non-uniform emission strength between the light emitting surfaces and the degradation in high temperature reliability during extended operation may still occur.
In a parallel type electrode structure in accordance with an embodiment as broadly described herein, the pad electrode 170 is positioned over the first insulating layer 150 and the first electrodes 160 are positioned over the light emitting surface. In this structure current applied to the pad electrode 170 flows to the first electrodes 160 of the light emitting surfaces, which are divided in four quadrants by the pad electrode 170 formed over the first insulating layer 150, then to the pad 170 and the first electrode 160 which contact each other in parallel, as shown in FIGS. 18 and 19.
The pad electrode 170 and the first electrode 160, which contact each other in parallel, may have the same current density (C) at each of the four divided light emitting surfaces such that a light emitting surface having a uniform emission strength may be achieved.
In addition, by isolating the relatively wider specific surface area, heat generated during extended high temperature operation may be more effectively dissipated, thus improving high temperature reliability and performance characteristics in applications such as BLU, and the like.
As the area of the light emitting device such as an LED is increased, driving the LED with a high current application scheme may benefit from improvement of the electrode structure. Therefore, the parallel type electrode structure as embodied and broadly described herein may be focused on the development of an electrode structure for a large area LED display device. The parallel type electrode as embodied and broadly described herein may be applied to a vertical type LED as well as a horizontal type LED, and may also be applied to an N-electrode as well as a P-electrode.
Hereinafter, a method for manufacturing a light emitting device according to an embodiment as broadly described herein will be discussed with reference to FIGS. 3 to 17.
First, a first substrate may be prepared (not shown in the Figures). The first substrate may be a sapphire (Al2O3) single crystal substrate, a SiC substrate, or the like, and is not limited thereto. A wet cleaning operation may be performed on the first substrate to remove impurities. Thereafter, the first conductive semiconductor layer 110 may be formed over, or on, the first substrate. This process will be described under the assumption that the first substrate is positioned over the first conductive semiconductor layer 110 based on the orientation shown in the drawings.
The first conductive semiconductor layer 110 may include an N type GaN layer formed by a Chemical Vapor Deposition (CVD) method, a Molecular Beam Epitaxy (MBE) method, a sputtering, or a Hydride Vapor Phase Epitaxy (HVPE) method, or other method as appropriate. Further, the first conductive semiconductor layer 110 may be formed by implanting silane gas (SiH4) including n type impurities, such as trimethyl gallium gas (TMGa), ammonia gas (NH3), nitrogen gas (N2), silicon (Si), and the like, in a chamber.
In alterative embodiments, an undoped semiconductor layer (not shown) may be formed over the first substrate, and the first conductive semiconductor layer 110 may be formed over the undoped semiconductor layer. For example, an undoped GaN layer may be formed over the first substrate.
After the first conductive semiconductor layer 110 is formed over the first substrate, the active layer 120 is formed over the first conductive semiconductor layer 110. The active layer 120 may be a layer that emits light having energy determined by a unique energy band of an activation (light emitting layer) material by impinging electrons injected through the first conductive semiconductor layer 110 and holes injected through the second conductive semiconductor layer 130. The active layer 120 may have a quantum well structure formed by alternately stacking a nitride semiconductor thin film layer having a different energy band one time or several times. For example, the active layer 120 may have a multi quantum well structure having an InGaN/GaN structure by implanting trimethyl gallium gas (TMGa), ammonia gas (NH3), nitrogen gas (N2), trimethyl indium gas (TMIn), but is not limited thereto.
Thereafter, the second conductive semiconductor layer 130 is formed over the active layer 120. For example, the second conductive semiconductor layer 130 may be formed in a P type GaN layer by implanting bicetyl cyclophentadienyl magnesium (EtCp2Mg) {Mg(C2H5C5H4)2 including p type impurities, such as trimethyl gallium gas (TMGa), ammonia gas (NH3), nitrogen gas (N2), magnesium (Mg), in a chamber, but is not limited thereto.
Next, a second electrode layer 140 is formed over the second conductive semiconductor layer 130. The second electrode layer 140 may include an ohmic layer 142 and a second substrate 144. The second electrode layer may also include a reflective layer 143 and a coupling layer 145. Simply for ease of illustration, the reflective layer 143 and the coupling layer 145 are only shown in FIG. 3B.
The second layer 140 may be formed by stacking a single metal, a metal alloy, a metal oxide, and the like, in plurality in order to effectively perform a hole injection. For example, the ohmic layer 142 may include at least one of ITO, IZO(In-ZnO), GZO(Ga-ZnO), AZO(Al-ZnO), AGZO(Al-Ga ZnO), IGZO(In-Ga ZnO), IrOx, RuOx, RuOx/ITO, Ni/IrOx/Au, or Ni/IrOx/Au/ITO, but is not limited to thereto.
When the second electrode layer 140 includes a reflective layer, such a reflective layer may be formed of a metal layer including Al, Ag, or an alloy including Al or Ag. These materials effectively reflect light generated from the active layer 120, making it possible to remarkably improve light extraction efficiency of the light emitting device.
Further, when the second electrode layer 140 includes a coupling layer, the reflective layer may also act as the coupling layer, or the coupling layer may be formed of nickel (Ni), or gold (Au), and may be provided in addition to or instead of the reflective layer.
The second layer 140 may include the second substrate 144. When the first conductive semiconductor layer 110 has a sufficient thickness of 50 or more, a process of forming the second substrate 144 may be omitted. In order to effectively inject holes, the second substrate 144 may be formed of a metal having excellent conductivity, a metal alloy, or a conductive semiconductor material. For example, the second substrate 144 may be copper (Cu), copper alloy, Si, Mo, SiGe, or the like. A method for forming the second substrate 144 may include a electrochemical metal deposition method, a bonding method using an eutectic metal, or other method as appropriate.
Thereafter, the first substrate may be removed so that the first conductive semiconductor layer 110 is exposed. A method for removing the first substrate may include a method of separating the first substrate using high-output laser or a chemical etching method. Further, the first substrate may be removed by being physically ground. Removing the first substrate exposes the first conductive semiconductor layer 110.
Hereinafter, a process of forming the first insulating layer 150 will be described with reference to FIGS. 5 to 12.
As shown in FIGS. 5 and 6, a first pattern 310 may be formed over the first conductive semiconductor layer 110. For example, the first pattern 310 may expose an area in which a trench may be formed with a photosensitive film or an insulating film. Portions of the first conductive semiconductor layer 110, the active layer 120, the second conductive semiconductor layer 130, and the second electrode layer 140 are removed along with a process of forming a trench T (see FIG. 7). Removal of the outer portions of the first conductive semiconductor layer 110, the active layer 120, the second conductive semiconductor layer 130, and the second electrode layer 140 allow for coupling of a second insulating layer 152 thereto. As shown in FIG. 3A, a portion of the outer portion of the ohmic layer 142 in the second electrode layer 140 may also be removed, but the embodiment is not limited thereto.
Next, as shown in FIGS. 7 and 8, a portion of the first conductive semiconductor layer 110, the active layer 120, and the second conductive semiconductor layer 130 may be etched using the first pattern 310 as an etch mask to form the trench T. For example, the trench T may be formed by dry or wet etching. The trench T may be a cross type as shown in FIG. 8, but is not limited thereto. The trench T separates the LED chip into a plurality of areas in various forms. In this embodiment, the trench T may be formed by being etched to the second conductive semiconductor layer 130. In certain embodiments, the trench T may also extend into a portion of the second electrode layer 140.
Subsequently, the first pattern 310 may be removed as shown in FIGS. 9 and 10. For example, the first pattern 310 may be removed by an ashing method, a wet etching method, or other method as appropriate.
Next, the first insulating layer 150 is formed as shown in FIGS. 11 and 12 to fill the trench T. For example, the first insulating layer 150 may be formed of insulating film such an oxide film or a nitride film. FIG. 11 is a cross-sectional view taken along line I-I' of FIG. 12.
The second insulating layer 152 surrounding the outer portions of the first conductive semiconductor layer 110, the active layer 120, and the second conductive semiconductor layer 130, may be formed along with the formation of the first insulating layer 150. For example, a passivation layer surrounding the outer portions of the first conductive semiconductor layer 110, the active layer 120, the second conductive semiconductor layer 130 may be formed of an insulating film such as an oxide film or a nitride film, etc.
Next, as shown in FIGS. 13 and 14, the first electrodes 160 are each formed over the separated first conductive semiconductor layer 110. FIG. 13 is a cross-sectional view taken along line II-II' of FIG. 14.
In this embodiment, the first electrode 160 contacts the first conductive semiconductor layer 110 over a wide range, but may be formed such that less of the first electrode 160 covers a portion of the first conductive semiconductor layer 110 from which light is emitted. In accordance with the invention, the first electrode 160 is formed as a grid.
Subsequently, as shown in FIGS. 15, 16, and 17, the pad electrode 170 by which the first electrodes 160 are connected to each other is formed over the first insulating layer 150. FIG. 15 is a cross-sectional view taken along line II-II' of FIG. 16 and FIG. 17 is a cross-sectional view taken along line III-III' of FIG. 16.
As shown in FIGS. 18 and 19, in the parallel type electrode as embodied and broadly described herein, which is a structure in which the pad electrode 170 is disposed over the first insulating layer 150 and the first electrodes 160 are disposed over the light emitting surface, current applied to the pad electrode 170 flows to the first electrodes 160 of the four divided light emitting surfaces formed over the first insulating layers 150. The pad electrode 170 and the first electrodes 160 contact each other in parallel. In this embodiment, the pad electrode 170 may be formed at the center of the upper surface of the light emitting structure, such that it may have substantially the same current density (C) at the separated light emitting surface.
Therefore, the pad electrode 170 and the first electrode 160, which contact each other in parallel, are distributed to have the same current density (C) at each of the four divided light emitting surfaces such that a light emitting surface having uniform emission strength may be achieved.
In a light emitting device as embodied and broadly described herein, the parallel type electrode structure may solve the current bottleneck phenomenon (crowd phenomenon) as well as provide smooth current spreading.
The parallel type electrode structure may also provide uniform current density over the light emitting area, and so the activation area may generate uniform emission strength over the entire area by the n-i-p junction, making it possible to obtain improved effect of light amount.
Further, a light emitting device as embodied and broadly described herein forms an isolation having a wide specific surface area, thereby achieving excellent heat dissipation. In addition, the isolation having the relatively wider specific surface area may provide improved heat dissipation, thus improving high temperature reliability during extended operation time and improving characteristics in applications such as BLU, etc.
A light emitting device is provided that is capable of solving a current bottleneck phenomenon, or crowd phenomenon, while smoothly spreading current.
A light emitting device is provided that has excellent heat dissipating characteristics by forming isolation having a wide specific surface area.
As described above, a light emitting device comprises light emitting structure having a second conductive semiconductor layer, an active layer and a first conductive semiconductor layer; and a parallel type electrode structure formed over the light emitting structure. The parallel type electrode structure is provided over the first conductive semiconductor layer. A second insulating layer surrounds the outer portions of the first conductive semiconductor layer, the active layer, and the second conductive semiconductor layer.
A first insulating layer separates the first conductive semiconductor layer, the active layer, the second conductive semiconductor layer into a plurality of areas. First electrodes are provided over the separated first conductive semiconductor layers. Each first electrode is separately provided over the separated first conductive semiconductor layer. The first electrode is provided over the separated first conductive semiconductor layer in a grid type.
A pad is provided over the first insulating layer. The pad may be provided at the center of the light emitting structure to connect the first electrodes. The pad is provided over the first insulating layer and the first electrode is over the light emitting surface. The current applied to the pad may flow into the first electrodes of the light emitting surfaces divided in four through the pad electrode over the first insulating layer, the pad and the first electrode contacting each other in parallel. The pad and the first electrode, which contact each other in parallel, may have the same current density at the light emitting surfaces divided in four.
Further, a light emitting device may comprise a light emitting structure that includes a second conductive semiconductor layer, an active layer, and a first conductive semiconductor layer; a first insulating layer that separates the first conductive semiconductor layer, the active layer, the second conductive semiconductor layer into a plurality of areas; a first electrodes over the separated first conductive semiconductor layers; and a pad that is over the first insulating layer to connect the first electrodes.
The first electrode is provided over the separated first conductive semiconductor layer in a grid type.
Each first electrode is separately provided over the separated first conductive semiconductor layer.
A portion of the outer portions of a the first conductive semiconductor layer, the active layer, and the second conductive
semiconductor layer is removed. A second insulating layer surrounds the outer portions of the first conductive semiconductor layer, the active layer, and the second conductive semiconductor layer.
The pad may be provided at the center of the light emitting structure to connect the first electrodes. The current applied to the pad may flow into the first electrodes of the light emitting surfaces divided in four through the pad electrode over the first insulating layer, the pad and the first electrode contacting each other in parallel. The pad and the first electrode, which contact each other in parallel, may have the same current density at the light emitting surfaces divided in four.

Claims

A light emitting device, comprising:
a plurality of light emitting elements arranged in a two-dimensional array and formed on a common second electrode layer (140) which is not separated for each light emitting element, each light emitting element including a first conductivity type layer (110), an active layer (120) and a second conductivity type layer (130), wherein the active layer is formed between the first conductivity type layer (110) and the second conductivity type layer (130);

a plurality of trenches (T) extending through the first conductivity type layer (110), the active layer (120) and the second conductivity type layer (130), thereby spearating adjacent light emitting elements of the plurality of light emitting elements;
a first insulating layer (150) formed in the trenches (T) between adjacent light emitting elements, wherein a top surface of the first insulating layer (150) is extended onto a top surface of each light emitting element;

a second insulating layer (152) on outer peripheral portions of the first conductivity type layer (110), the active layer (120), and the second conductivity type layer (130) wherein a top surface of the second insulating layer (152) is extended onto a top edge surface of each light emitting element,

first electrodes (160), each formed as a grid and respectively disposed on a respective one of the plurality of light emitting elements; and

a pad electrode (170) electrically connected to the first electrodes,

wherein the pad electrode is disposed on the first insulating layer,

wherein the pad electrode (170) comprises a central portion which is disposed on the top surface of the first insulating layer (150) such that it covers the trenches (T), wherein a width of the central portion is less than a width of the first insulating layer (150)

wherein the pad electrode (170) further comprises a plurality of branch portions extending from the central portion to the first electrodes (160) and

wherein a portion of the branch portions of the pad electrode (170) is vertically overlapped with the first electrodes (160), and wherein the plurality of branch portions of the pad electrode (170) contacts each of the grids formed by the first electrodes (160).
The light emitting device of claim 1, wherein overlapped portions between the branch portions and the first electrodes (160) have at least two portions spaced apart from each other.
The light emitting device of claim 1 or claim 2, wherein the second insulating layer (152) surrounds the plurality of light emitting elements.
The light emitting device of any one of claim 1 to 3, wherein each electrode of the first electrodes (160) is formed on a corresponding portion of the first conductivity type layer (110) of the light emitting element.
The light emitting device of any one of claims 1 to 4, wherein the plurality of light emitting elements are substantially co-planar on the common second electrode layer (140).
The light emitting device according to any one of claims 1 to 5, wherein the pad electrode (170) is located substantially at a center of the plurality of light emitting elements.
The light emitting device of any one of claims 1 to 6, wherein the first electrodes (160) of adjacent light emitting elements are formed to be complementary in shape.
A method of making a light emitting element, the method comprising:
forming a plurality of light emitting elements, including forming a first conductivity type layer (110), forming an active layer (120) on the first conductivity type layer (110) and
forming a second conductivity type layer (130) on the active layer (120);

providing a common second electrode layer (140) on the second conductivity type layer (130), the plurality of light emitting elements being arranged in a two-dimensional array and formed on the common second electrode layer (140) which is not separated for each light emitting element;

forming a plurality of trenches (T) through the first conductivity type layer (110) and the active layer (120) thereby separating adjacent light emitting elements;

forming a first insulating layer (150) in the trenches so as to isolate the plurality of light emitting elements, a top surface of the first insulating layer (150) extending onto a top surface of each light emitting element;

providing a second insulating layer (152) surrounding an outer peripheral portion of the first conductivity type layer, the active layer and the second conductivity type layer, a top surface of the second insulating layer (152) extending onto a top surface of each light emitting element;

respectively forming a plurality of first electrodes (160) on the plurality of light emitting elements, each first electrode (160) formed as a grid; and
forming a pad electrode (170) to couple the first electrodes (160) on the first insulating layer (150), the pad electrode (170) comprising a central portion disposed on the top surface of the first insulating layer (150) such that it covers the trenches (T), wherein a width of the central portion is less than that of the first insulating layer (150), the pad electrode (170) further comprising a plurality of branch portions extending from the central portion to the first electrodes (160),

wherein a portion of the branch portion of the pad electrode (170) is vertically overlapped with and electrically connected to the first electrodes (160).
The method of claim 8, wherein overlapped portions between the branch portions and the first electrodes (160) have at least two portions spaced apart each other.
The method of claim 8 or 9, wherein the second insulating layer (152) surrounds the plurality of light emitting elements.
The method of any one of claims 8 to 10, wherein providing the common second electrode layer (140) on the second conductivity type layer (130) comprises:
providing an ohmic layer on the second conductivity type layer; and

providing a substrate on a side of the ohmic layer opposite the second conductivity type layer.
The method of any one of claims 8 to 11, wherein forming the trenches through the first conductivity type layer (110) and the active layer (120) further comprises extending the trenches (T) through the second conductivity type layer (130) and into the ohmic layer.
The method of any one of claims 8 to 12, wherein the plurality of branch portions of the pad electrode (170) contacts each of the grids formed by the first electrodes (160).